The invention relates to a method for detecting a switched state of a switch.
In order to reduce the consumption of current in battery-operated electrical systems, in the virtually completely switched-off state, which is also referred to as a stand-by mode, only the switches which, when actuated, cause the system to be activated, are interrogated by applying an interrogation current to them. In order to be able to carry out a sufficiently precise interrogation of the switches, a switched state of the switch must be carried out with high electrical interrogation currents. This results in relatively high quiescent currents in the stand-by mode of battery-operated systems and can cause predefined quiescent current conditions to be exceeded.
In a known device, disclosed in German Patent DE 43 37 273 C2, for reducing the quiescent current in deactivated motor vehicles, a controllable switch for disconnecting loads of the electrical system from a motor vehicle battery is opened if a fault is detected in a load in the electrical system which, when the controllable switch is closed, could lead to a quiescent current which is higher than a predefined quiescent current threshold or its value is higher than a threshold value corresponding to a predefined quiescent current threshold.
In the known device, layers, for example an oxide layer, which constitute an additional electrical resistance are formed on the switch contacts of the switch which is opened for a relatively long time. This makes reliable switching of the switch possible only to a limited degree. A switch interrogation must be carried out with a relatively high electrical current in such a case.
In a further known method for interrogating switch positions switches are placed in the on and off states under the control of a microprocessor (see Published, Non-Prosecuted German Patent Application DE 40 15 271 A1). In the on state, the constant switch current that flows in this state is evaluated by the microprocessor. The negative influence of disruptive oxide layers cannot be eliminated here.
German Patent DE 199 15 973 C1 merely discloses that the voltage is lowered in order to reduce the consumption of current. However, a switched state interrogation of a switch does not take place here.
It is accordingly an object of the invention to provide a method for detecting a switched state of a switch that overcomes the above-mentioned disadvantages of the prior art methods of this general type, which can be carried out easily and which permits reliable switching of a switch.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for detecting a switched state of a switch. The method includes electrically connecting the switch to a voltage source and, when the switch is in a closed switch position, a high electrical interrogation current flows which is higher than or equal to a first current threshold value. The switched state of the switch is detected by evaluating a voltage or a current at the switch. A low interrogation current that is lower than or equal to a second current threshold value is electrically connected to the switch after the closed switch position is detected. The low interrogation current is supplied for a time period that starts at a time at which the closed switch position of the switch is detected. The first current threshold value is higher than the second current threshold value. The low interrogation current that flows when the switch is closed is increased to a value that is equal to or higher than the first current threshold value only after the time period has expired. The time period is dependent on operating conditions and/or ambient conditions of the switch.
According to the invention, in a method for detecting a switched state of a switch when the switch is closed, an interrogation current is impressed which is higher than or equal to a first current threshold value. The detection of the switched state of the switch is carried out here by evaluating a current and/or a voltage at the switch. If a closed switch is detected, when the switch is closed an interrogation current is impressed, which is lower than or equal to a second current threshold value, for a time period is which starts at the time at which a closed switched state of the switch is detect or for a number of interrogations of the switched state of the switch which is counted starting from the detection of the closed switch. The interrogation current which flows when the switch is closed is not increased again to a value which is higher than or equal to the first current threshold value until the time period or the number of interrogations of the switch position is reached. There is provision here for the time period within which the interrogation with the interrogation current is carried out to be defined as a function of operating and/or ambient conditions of the switch.
As a result, it is possible to ensure that reliable detection of the switch position and reliable switching of the switch are possible.
There may be provision for the number of interrogations of the switch position of the switch that is counted starting from the detection of a closed switch position to be made dependent on operating and/or ambient conditions.
As a result it is possible to ensure that reliable detection of a switched state and reliable switching of the switch are possible even if the layer which produces an additional electrical resistance is formed at differing rates on the switch contacts.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for detecting a switched state of a switch. The method includes electrically connecting the switch to a voltage source and, when the switch is in a closed switch position, a high electrical interrogation current flows which is higher than or equal to a first current threshold value. The switched state of the switch is detected by evaluating a voltage and/or a current at the switch. A low interrogation current that is lower than or equal to a second current threshold value is electrically connected to the switch when the closed switch position is detected. The low interrogation current is supplied for a number of interrogations of a switch position of the switch that is counted starting from a detection of the closed switch position. The first current threshold value is higher than the second current threshold value. The low interrogation current that flows when the switch is closed is increased again to a value that is equal to or higher than the first current threshold value only after the number of interrogations of the switch position has been reached.
In accordance with an added mode of the invention, there is the step of setting the number of interrogations of the switched position of the switch that are counted starting from the detection of the closed switch position in dependence on operating conditions and/or ambient conditions of the switch.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for detecting a switched state of a switch, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.